You are only permitted to ask one question, so I have had to edit your question down. It is clear that change is a key theme in this remarkable novel, as it presents us with a distinct African culture which has remained unchanged for a very long time. It is of course the arrival of white men in the form of colonial powers that bring a massive change to this world and rupture many of the traditions and rituals that are perceived to be "wrong" from the white men's point of view. A classic example of this is polygamy, where it is absolutely fine for Okonkwo to have many wives, but from the colonialists' perspective, this is deemed to be "wrong". The novel in part traces these massive cultural conflicts.

The song you have highlighted in Chapter 12 thus represents the culture and traditions of the tribe as they have existed for centuries. It is clear that the music is part of this ritual of marriage, as is the arrival of the bride holding a cock in her hand. The words of the song seem to represent the blushing bride's modesty, but at the same time, her willingness to be admired, desired and lusted after, for when direct touch occurs, she forbids it, but when the waist beads are held, this is permitted.

The conflict between tradition and change, therefore, is highlighted in this episode by the narration of a typical wedding ritual in the culture of Okonkwo's tribe.